Sedimentation–diffusion dynamics in colloid–polymer mixtures

We show experimentally how a phase separated colloid–polymer mixture finds its sedimentation–diffusion equilibrium after initial fluid–fluid demixing. During this equilibration process we measure key parameters of the colloidal interface by assuming local mechanical equilibrium and we inspect the behaviour of the meniscus close to a vertical wall. It turns out that the kinetic pathway associated with the sedimentation process not only strongly depends on the overall colloid and polymer concentrations but also on the height of the suspension. Beyond a certain height the system locally passes through the gas–liquid critical point, which opens new ways to study critical phenomena